The present application relates to a laser diode element assembly and a method of driving the same.
Recently, for researches in a leading-edge science region using laser light of pulse duration in the attosecond range or the femtosecond range, ultrashort-pulse/ultrahigh-power lasers have been frequently used. Moreover, a high-power/ultrashort-pulse laser diode element with a light emission wavelength of 405 nm made of a GaN-based compound semiconductor is expected to serve as a light source of a volumetric optical disk system which is expected as a next-generation optical disk system following a Blu-ray optical disk system, or a light source necessary in the medical field, the bio-imaging field, or the like.
As the ultrashort-pulse/ultrahigh-power laser, for example, a titanium/sapphire laser is known; however, the titanium/sapphire laser is an expensive and large solid laser light source, which is a main impediment to the spread of the technology. If the ultrashort-pulse/ultrahigh-power laser is realized through the use of a laser diode or a laser diode element, it is considered that a large reduction in size, price, and power consumption of the ultrashort-pulse/ultrahigh-power laser, and high stability of the ultrashort-pulse/ultrahigh-power laser will be achieved, thereby leading to a breakthrough in promoting widespread use of the ultrashort-pulse/ultrahigh-power laser in these fields.
On the other hand, an attempt to shorten pulses from a laser diode element has been actively studied since 1960s in the communications field. As a method of generating short pulses in a laser diode element, a gain switching method, a loss switching method (a Q switching method), and a mode-locking method are known, and in these methods, the laser diode element is combined with a semiconductor amplifier, a nonlinear optical element, an optical fiber, or the like to aim at achieving higher power. Mode-locking is further classified into active mode-locking and passive mode-locking. To generate optical pulses based on the active mode-locking, an external resonator structure is configured of a laser diode element with use of a mirror or a lens, and radio-frequency (RF) modulation is applied to the laser diode element. On the other hand, in the passive mode-locking, when a laser diode element with a multielectrode structure is used, optical pulses are allowed to be generated by a simple DC drive.
In laser light sources, achieving higher power is a major issue. In addition, for the convenience of using the laser diode element as a light source, it is frequently desired that laser light emitted from the laser diode element be single-mode light. These issues are major issues in not only pulsed oscillation of laser light but also continuous-wave oscillation. As a method of amplifying light from a laser light source, a semiconductor optical amplifier (SOA) is considered. Herein, the optical amplifier is an amplifier which directly amplifies an optical signal in the form of light without converting the optical signal into an electrical signal, and the optical amplifier has a laser structure without a resonator, and amplifies incident light by an optical gain thereof. However, to reduce manufacturing cost, a light source with a simple configuration without optical components such as an optical amplifier is strongly desired.